Almost all animals with complex nervous systems, including mammals, birds, fish and reptiles, have a brain, but we are still far from fully understanding which parts of the brain do what. This is partly because certain tasks activate neurons in the brain that work together to solve problems.
Two research recently published in Nature document the work of a consortium of 12 laboratories covering 279 regions of the mouse brain to gain a better understanding of how to map the human brain.
Similarities between mouse and human brains
For this study, the researchers used tiny electrodes attached to the brain to record the firing of hundreds of neurons simultaneously. Each of the 12 laboratories performed the same experiment and recorded part of the target brain region in 139 mice.
“We can finally get a global view of what's going on in the brain and see how all the different regions contribute to solving a problem,” says Alexandre Pougetco-author of the study, co-founder of the International Brain Laboratory and professor at the University of Geneva.
The mouse brain and the human brain are similar and different in some really important ways. The human brain is much larger, but there are many similarities, especially in the type of tasks the mice performed in the study.
In both humans and mice, light enters the retina, reaches the thalamus, and ultimately reaches cortical and subcortical structures. But there are certain features of the visual system that mice do not have, says the author of the joint study. Anne K. Churchland and a neuroscientist at the University of California, Los Angeles.
“We've been very careful about the differences between mice and humans because ultimately we want to make findings that will impact human health,” Churchland says.
As a result, the researchers designed a task that “resembled” human behavior. To perform this task, mice looked at the screen and used a toy steering wheel to pinpoint an object and move it to the center of the screen. It was similar to how people play video games. If the mouse completed the task correctly, it received a reward. Tiny helmets equipped with electrodes showed which part of the brain was involved in decision-making.
How humans and mice make decisions
Whenever mice make decisions, they combine what they already know about a subject with sensory details to help them make a decision. People do pretty much the same thing.
For example, if you live in a place where it never rains, you probably won't take an umbrella with you, even if it's cloudy outside. And if you live in a place where it rains constantly and it's cloudy outside, you're much more likely to make a decision based on prior knowledge to take an umbrella with you.
“It's the same sensory evidence, but your previous belief is completely different,” Churchland says.
The mice's preliminary data would be how many times the stimulus occurred on the left side rather than the right side, or vice versa. Especially when the task was more difficult to complete, the mice used prior knowledge to predict where the stimuli would appear next.
It is important to be able to observe multiple parts of the brain at the same time to see how many parts of the brain are involved in decision making. The study of 279 parts of the brain allowed the researchers to see which parts of the brain were used to make decisions based on prior beliefs.
A map of the brain that has been in the works for the past seven years shows that many more areas of the brain are used when making simple decisions than scientists previously thought.
“We were surprised by the breadth of areas regulated by animal choice,” Churchland says.
Read more: Understanding memory and storage in the brain
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